In such retention devices it is important that they be proof against inadvertent operation, either by the wearer or as a result of the adverse conditions they may encounter whilst wearing such a helmet and mask combination. It is also important for such devices to be easy to operate and release in an emergency and it is also important that they do not cause injury to the wearer or damage to the helmet or other protective clothing worn by the person. Known button and stud devices have not been found to be satisfactory for particularly demanding applications such as those encountered by aircrew during ejection or parachutists where adverse conditions such as very high `g` loadings and air blast conditions are encountered.
In known systems worn by, for example, aircrew there is provided a hook and eye system for retaining masks, the hook being attached by a threaded rod to the helmet, the threaded rod providing an adjustment means for adjusting the tension of the mask. The mask is retained by cable or chain means connected to a mask retaining eye engagable with the helmet mounted hook. Such systems are not easy to operate and are prone to inadvertent disconnection under certain conditions.